モデル実験による底吹き羽口におけるバックアタック現象の発生メカニズムの検討

抄録

The "back-attack" phenomenon was suspected to be an important factor in tuyere refractory erosion, so the characteristics of submerged high speed gas jet were investigated in a water model, and the mechanism of the back-attack generation was clarified.
1) The submerged gas jet forms a cavity in the bath, but occasionally the cavity is constricted close to the tuyere, and collapses, so the jet blows back and attacks the surface of the tuyere. That is named "back-attack" phenomenon. This constriction is thought to be caused by the suction, because the static pressure distribution shows large negative value there. Therefore not only the surrounding gas, but also the liquid is drawn into the negative depression of static pressure.
2) The velocity of the jet blown in water at the pressure 3.84 bar through the straight type tuyere reached sonic velocity at the exit of the tuyere and increased suddenly to super sonic value after exceeding the tuyere. Mach number distribution showed large up-and-down change and formed supersonic core inZ/D from 0 to 7, and the super sonic region continued to Z/D of 12.8 where Z is distance from the tip of the tuyere along the tuyere centerline and D is inner diameter of the tuyere. The value of Mach number of the gas jet in water showed good agreement with that in air before the exit of the tuyere, but decayed more rapidly than the air jet after leaving the tuyere, because the gas jet in water was pushed in the cavity and cavity collapsed intermittently.